Sources
All the different types of water pollution fall into two groups called point pollution and non-point pollution.

Point pollution occurs when harmful substances are discharged directly into a body of water and the source, or point, of the pollution can be clearly identified. Examples would include an oil spill from a tanker like the Exxon Valdez incident of 1989 or a sewer system overflowing and dumping untreated waste into a river.

Non-point pollution occurs when harmful substances enter the water in a watershed through runoff or through seepage that occurs after pollutants sink into the ground. Non-point pollution comes from more than one source and more than one place. It accounts for most of the contamination in rivers, lakes and wetlands. Because it can affect areas far from the original source, it is much more difficult to control. From motor oil to fertilizers to pesticides to trash, everyday people are responsible for most non-point pollution. That is why every person has a huge responsibility to control non-point pollution.

Trash/Plastics: Trash is a huge problem in waterways and plastic trash is a very big issue. In the United States alone people empty an average of 2.5 million plastic water bottles AN HOUR, and only 10 percent of these get recycled. Many improperly disposed plastics end up in waterways and the ocean. When plastics degrade, they end up as tiny chemical polymers that never go away. Plankton and jellyfish eat these these polymers, and some places in the ocean have now been shown to have a ratio of 60 percent plastic polymers to 40 percent plankton. Bigger pieces of plastic are eaten by sea birds, turtles, and other wildlife.

Sediments and Solids: When soil or sediments are washed into bodies of water by rain or runoff, they clog the water with sediments that make breathing hard for animals or plants that live in the water. They also fill in waterways when the sediments sink to the bottom, a process called “eutrophication” (YOU-tro-fik-AY-shun).

Nutrients: An overabundance of nutrients for plant life might seem like a good thing. But it is one of the most damaging forms of water pollution. Sewage and farm fertilizers contain nutrients such as nitrates and phosphates that cause extreme growth of plants like algae that live in waterways. When overfed plants “bloom” like this, they use up dissolved oxygen as they decompose, starving fish and other organisms of the element they need to breathe.

Organic Pathogens: Pathogens are things that make people or animals sick. Organic pathogens are living organisms such as bacteria or viruses that can cause illnesses ranging from typhoid to dysentery to respiratory diseases. These enter waterways from untreated sewage, storm drains, septic tanks, farms and boats that dump untreated sewage in lakes or the ocean.

Chemical Pathogens: Chemicals that get into watersheds from factory discharges, improper disposal or runoff have been shown to cause cancer and other diseases. In the 1970s, scientists discovered a connection between factories that manufactured electrical equipment, such as transformers, and PCBs, a harmful cancer-causing chemical. The improperly disposed PCBs were finding their way into waterways next to the factories and negatively affecting wildlife. Although PCBs are no longer in widespread use, traces of the chemical still remain in many waterways.

Radioactivity: Radioactive substances are given off in the form of waste from nuclear power plants and from industrial, medical and scientific uses of radioactive materials. When radioactivity gets into the water system, it remains there for thousands of years.

Heat: Heat is often overlooked as a source of water pollution. Many industries use water to cool machinery or products. Even if it is not contaminated by chemicals or other materials, it can alter the environment when it is discharged by raising the natural temperature of waterways. This can be damaging or fatal to both plants and wildlife.

Dead Zones: Dead zones are places in the ocean where there isn’t enough oxygen to support sea life. They are caused by non-point pollution. How does this happen? Too much phosphorus, nitrogen and waste in the water from fertilizers, pesticides and animals cause algae “blooms” which use up the available oxygen in the water along coasts. Every year, an enormous dead zone forms in the Gulf of Mexico near the mouth of the Mississippi River. Why there? The Mississippi is where watersheds from 40 percent of the United States drain into the ocean.